Hearing aid noise suppression system

Abstract

A hearing aid responds to increased noise by changing its frequency response to reduce the effects of the noise. The hearing aid has a circuit which varies the frequency response of the unit as a function of low-frequency sounds, using a fast attack time and a much slower release time.

We claim: 
     
       1. A hearing aid circuit, comprising: a high-pass filter with adjustable frequency response;   a bandpass filter; and   an attack and release circuit connecting the bandpass filter to the high-pass filter in a manner that an increased output from the bandpass filter changes the frequency response of the high-pass filter after an attack time and a decreased output from the bandpass filter changes the frequency response of the high-pass filter after a release time which is much longer than said attack time.   
     
     
       2. The hearing aid circuit of claim 1, wherein said high-pass filter comprises a filter capacitor and said attack and release circuit comprises a transistor with its collector-emitter circuit shunting said filter capacitor. 
     
     
       3. The hearing aid circuit of claim 2, wherein said attack and release circuit further comprises a timing capacitor which is connected to the base of said transistor, a charging resistor through which said timing capacitor is clamped, and a discharging resistor thereof which said timing capacitor is discharged, said charging resistor having a lower resistance than said discharging resistor.